The homophobia is that the "joke" here is "hahah trump is GAY with BILL CLINTON!"
Gayness isnt a bad thing. Using it to be insulting to trump means in that instance its perceived as a bad thing. Thats the homophobia.
Trump is an awful person who has done awful things. "Haha gaaay" isnt useful or funny when the man is a serial rapist, and now murderer